ALL REAGENTS Chapters 9-15 and Mechanism Pathways

A set of vocabulary flashcards covering key terms and concepts from Chapter 9 of the lecture notes, focusing on organic reactions, reagents, and mechanisms.

HOW TO STUDY

1) What is the starting material:

In this case, OH is the starting material (ALL OF CHAPTER 9)

2) What is the reagent?

What causes that reaction to happen to convert start to end product

3) What is the end product?

What causes the reaction to occur

-Alkoxide Reaction

-Double Bond formed

-Substitution Formed

-What is the leaving group? Good or Bad?

-How many carbons are attached to the OH?

-Any carbocation rearrangements?

4) Look at the end product first and then the starting product for retrosynthesis

CHAPTER 9 Reagents

1) Reagent: Na+OH-

2) Na+H-

2a) Na+H-
Path #1: Alkoxide —> Ether

2b) Na+H-
Path#2: Alkoxide → Epoxide

A reagent used for converting alcohols into chlorides, often used in organic synthesis.

3) H2SO4

Acid Catalyzed Dehydration

3a) H2SO4
Path #1: E1 Mechanism with 2° and 3° R-OH

Acid Catalyzed Dehydration

3b) H2SO4
Path #2: E2 Mechanism with 1° R-OH

Acid Catalyzed Dehydration

4) H-x (X= I, Br, Cl)

4a) H-X
Path #1: 1° ROH + HX —> SN2 Mechanism

4b) H-X
Path #2: 2° or 3° ROH + HX —> SN1 Mechanism

SN1 Mechanism

#5) SOCl2 (thionyl chlroide) + pyridine

1° and 2° only
SN2 Mechanism

So chemists prefer SOCl₂ or PBr₃ when they want clean substitution without rearranging the carbon skeleton.

#6) PbBr3

So chemists prefer SOCl₂ or PBr₃ when they want clean substitution without rearranging the carbon skeleton.

What’s the difference between using an H-X (X= Cl, Br) for substitution instead of using SOCl2 and PBr3 as reagents. What about Vice Versa? Which reagent should I use in which situation? Do some scenarios have the same product using both types of reagents?

Quick exam shortcut

Alcohol type	Best reagent
1° alcohol	SOCl₂ or PBr₃
2° alcohol	SOCl₂ or PBr₃ (to avoid rearrangement)
3° alcohol	HX (HCl or HBr)

• HX → SN1 (good for 3° alcohols, rearrangements possible)

• SOCl₂ / PBr₃ → SN2 (best for 1° and 2°, no rearrangements

1. Using HX (HCl, HBr)

Examples: Hydrochloric acid and Hydrobromic acid

Mechanism depends on the alcohol

3° alcohol

• Reaction proceeds via SN1

• Forms a carbocation

• Rearrangements can occur

2° alcohol

• Often SN1, sometimes mixed mechanisms

• Rearrangements possible

1° alcohol

• Usually SN2

• Rearrangements usually don’t occur

Pros

✔ Works well for tertiary alcohols
✔ Simple reagent

Cons

❌ Carbocation rearrangements possible
❌ Strong acidic conditions can cause elimination (alkenes)

---

2. Using SOCl₂ or PBr₃

• Thionyl chloride converts alcohol → alkyl chloride

• Phosphorus tribromide converts alcohol → alkyl bromide

Mechanism

• Usually SN2

• No carbocation intermediate

Pros

✔ No rearrangements
✔ Very clean reactions
✔ Excellent for 1° and 2° alcohols

Cons

❌ 3° alcohols don’t work well (SN2 is blocked by sterics)

#7) TsCl pyridine

OH → OTS → back to OH using Na+OH- substitution

OTS keeps its retention of stereochemistry!!!!!

#8) Ether → Reagent: 2 HX equivalents

KEEP OH on the least substituted R and (X = Br, Cl, I) on most substituted R for 3° carbocation forms

If none, then KEEP OH on most substituted R and (X = Br, Cl, I) on least substitued R for methyl or 1° least hindered

Form carbocation 1st , if possible.

• If only 1° and/or methyl, then least hindered is attacked 1st

The first H-X attacks and protonates the MOST STABLE substituent which is 3°!

If there is no 3°, then protonate the LEAST susbtituent R group of the ether….EVEN IF you have a scenario with a 2° and a 1° R group,…. choose the 1° R group first to protoante using the H-X

NOTE: if there is a Phenoyl benzene ring with double bond resonance, KEEP IN THE ETHER!! H-X does not protonate sp2 hybridized carbons only sp3 hybridized carbons yoooo.

#9 Epoxide Opening:

Reagent: Strong Nuc: OH-, OR-, CN-, SR-

SN2 Mechanism

Nuc Attacks Less Substituted Carbon

#10) Acid Catalyzed Opening

H2SO4, HI, HBr, HCl

#10b) Cyclohexane Epoxide Opening

1) Na+, OH-, CN-, OR- SR-,

2) H2O

Chapter 10 Alkene Reagents

STARTING MATERIAL IS ALKENES! REMEMBER THAT! Some reagents are the same as OH reagents but the starting material is different in this case.

Overview

Dehydrohalogenation: E2 Reaction

Dehydration: E1 Reaction

#1) Reagent: Alkene + H-X

Hydrohalogenation

Markovnikov’s Rule

X (Cl, Br, I) rotates robot arm to more substituted carbon and H rotates robot arm to less substitutd carbon

#2) Alkene + H20 + H2SO4

Hydration

#3) Alkene + X-X

Halogenation

ANTI ADDITION

#4) X-X + H2O

HaloHydrin Formation

ANTI ADDITION

#4b) NBS (N-bromosuccinide)

ANTI addition

#5) 1: BH3. 2: H2O2 OH-

Hydroboration Oxidation

-DONT Need to Know Mechanism

-Transition State

-Syn Addition

-Retention of Configuration

ANTI Markovnikov

-H goes on MOST SUBSTITUED CARBON

Chapter 11 Alkynes

Alyne Preparation and Formation

2NaNH2

Alkene → Br2 → 2NaNH2 → Alkyne

#1) Alkyne + HBr (2 times)

Hydrohalogenation

#2) Alkyne + X-X (2 times)

#3) Hydration (H20H2SO4)

#4) Hydroboration Oxidation (BH3 and H2O2 and OH-)

#5) Terminal Alkyne Reactions

-NaNH2- (strong base)

-NaH- (strong bases)

Forms Acetylide Ion

#6) 2 Ways to Make C-C bond

1) Na+ Cn-, H2O

2) New Acetylide Anion

#12 Oxidation and Reduction

OIL RIG

Oxidation is Losing electrons/C-H bonds

Reduction is Gaining electrons/C-H bonds

Reduction

High → Low oxidation state

Decrease # of C double bond C, C-O bonds, C-N, and C-X bonds (X = Cl, Br, I)

Increase # C-H bonds

Oxidation

Low → High Oxidation State

Decrease # C-H bonds

Incease # of C double bond C, C-O bonds, C-N, and C-X bonds (X = Cl, Br, I)

Oxidation State

THE AMOUNT OF OXIDATION OR A LOT OF C double bond C, C-O bonds, C-N, and C-X bonds (X = Cl, Br, I)

1) Reagent: Pd/C, H2

Reduction of Alkenes

1b) Reagent: Pd/C, H2

Reduction of Carbonyls

1c) Reagent: Pd/C, H2

Reduction of Aldehydes and Ketones form the C double bond O. The H attaches to the Oxygen first and then to the nearby carbon.

1d) Reagent Pd/C, H2

Reduction of alkynes

2) Lindlar’s Catalyst, H2

Reduction of Alkynes

Cis Alkene

3) Na°, NH3

Reduction of Alkynes

Trans Alkene

4) LiAlH4

Reduction of Polar C-X Bonds (Alkyl Halides)

SN2 Mechanism (INVERSION of STEREOCHEMISRY) using H as nucleophile

5) mPCBA

SYN ADDITION

Cis Alkene: Meso Cmpound and Identical (Superimposable mirror Images)

Trans Alkene: Enantiomers (50%/50%) (Non superimposable Mirror Images)

6)

1) KMnO4

2) H2O, KOH.

OR

1) OSO4.

2) NaHSO3, H2O

Dihydroxylation

SKIP MECHANISM FOR BOTH

Syn Addition for Both Cis and Trans Alkenes

#7 1) MCPBA. 2) H2SO4, H2O

AntiDehydroxylation

Know these Mechanism from Chapter 9 and Earlier from Chapter 12

#8.
1) O3 (Ozone)

2) H3C - S - CH3. (Dimethyl Sulfide)

OZONOLYSIS

Oxidative Cleavage of ALKENES

Skip Mechanism

1 to 2 molecules

If Cyclohexane → Unwind it

#8b)

1) O3 (Ozone)

2) H3C - S - CH3. (Dimethyl Sulfide)

OZONOLYSIS

Oxidative Cleavage of ALKYNES

#9:

1) K2Cr2O7

2) H20, H2SO4

OR

1) PCC

2° Alcohols

#9b)

1) K2Cr2O7

2)H20, H2SO4

OR

PCC

1° Alcohols

Chapter 13 Radicals

-single unpaired electron

-homolysis

-parallels carbocation stability

-more attached carbons = more stable

-3° > 2° > 1°

-NO REARRANGEMENTS like carbocations

General Features of Radical Reactions

Halogenation of Alkanes

Hydrohalogenation of Alkenes

#1) hv or ∆

Initiation

Propogation

Chlorination vs. Bromination

Chlorination:

-smaller

-less polarizable

-less stable

-Reacts quickly WITHOUT selecting just right bond

-UNSELECTIVE mixture of products

-FASTER

Bromination:

-larger

-more polarizable

-more stable

-takes its time to make JUST the RIGHT PRODUCT

-SELECTIVE, one major product

-Slower

-More Substituted C-H bond is weakest and easiest to break

BR2:

1:99

1 = Anti-Markovnikov

99 = Markovnikov

Cl2:

1 = Anti-Markovnikov

1 = Markovnikov

#2: H-Br hv or ∆ or ROOH

Radical Addition Reactions to Alkenes

Initiation:

Propogation:

Termination:

Chapter 14: Conjugation

Overlapping p orbitals on at least 3 adjacent atoms

Electrons in pi bond spread over a great area = stabilizatioin!

Allylic carbocation more stable than non allylic carbocation

Carbocation Stability:

1°< 2 = allylic carbocatioin < 3°

Benzylic carbocation more stable than non-allylic carbocation.

Delocalization = Stability

Common Examples of Resonance

1) Allyl System

-lone pair one sigma bond away from a double bond

2) Conjugated Double Bond

3) Cations adjacent to Lone pair

4) Double Bond with Adjacent Atoms differing in electronegativity

The Resonance Hybrid: Most closely resembles best hybrid

#1: Resonance structure with more bonds and fewer charges is better

#2: Resonance structure with every atom having an octet is better

#3: Resonance structure with negative charge on the more electronegative

atom is better.

Honorable Mention: Electrophilic Addition: 1,2- vs 1,4-Addition. When there is conjugation of 2 double bonds adjacent to each other in trans position

H-Br

-1,2 Addition: Major Product is Markovnikov

-1,4 Addition: Resonance Minor Product is Anti Markovnikov

#1: ∆

The Diels Alder Reaction

DIENE + DIENOPHILE

-exothermic

-2 sigma bonds formed and 1 pi bond formed from 3 pi bonds

1. Rotate diene to s-cis conformation.

-Diene must be in s-cis conformation:

-Dienes constrained to s-cis conformation are most reactive.

2. Draw dienophile adjacent to s-cis diene.

-Dienophile reactivity:

-Electron-withdrawing substituents on dienophile increase the reaction rate.

-More oxygen groups C double bond O

3. Break 3 π bonds. Show where new bonds form with arrow.

-Stereochemistry of dienophile is retained in the product:

-CIS-Dienophile → SAME COMPOUND and CIS SUbstituents

-TRANS-Dienoophile → Enantiomers and TRANS Substituents

Retrosynthetic Analysis of the Diels-Alder Reaction

1. Find the 6-membered ring containing C=C.

2. Draw 3 arrows, beginning at the π bonds.

3. Draw the diene and dienophile.

Chapter 15: Aromaticity

• All C-C bond lengths are equal.

• Planar

• 6 Cs and 6 Hs

Molecule must be:

1. Cyclic

2. Planar

3. Completely conjugated

4. Have a particular # of π electrons (4n+2)

Aromatic compound: 4N + 2 number of electrons (STABLE)

Antiaromatic compound: 4N number of electrons (NOT STABLE)